On 2017-01-30 03:27, Chris Angelico wrote:
On Mon, Jan 30, 2017 at 1:49 PM, Steve D'Aprano
<steve+pyt...@pearwood.info> wrote:
This code contains a Time Of Check to Time Of Use bug:
if os.path.exists(destination)
raise ValueError('destination already exists')
os.rename(oldname, destination)
In the microsecond between checking for the existence of the destination and
actually doing the rename, it is possible that another process may create
the destination, resulting in data loss.
Apart from keeping my fingers crossed, how should I fix this TOCTOU bug?
The Linux kernel (sorry, I don't know about others) provides a
renameat2() system call that has the option of failing if the
destination exists. However, I can't currently see any way to call
that from CPython. Seems like an excellent feature request - another
keyword-only argument for os.rename(), like the directory file
descriptors.
On Windows it raises FileExistsError if the destination already exists.
shutil.move, on the other hand, replaces if the destination already exists.
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